USING GIS TO GENERATE MUTUALLY EXCLUSIVE SERVICE AREAS LINKING TRAVEL ON AND OFF A NETWORK

Generating a buffer or service area around a feature is a very basic command of a geographic information system (GIS). However, most existing methods for doing so create simple distance-bounded geometric buffers. While these methods function well for many applications, they have limitations when dealing with network-based phenomena because they do not take the geometry or impedance of the underlying network into account. More complex methods can be used to create network-based service areas. While they tend to work well on the network itself, they often do not allocate off-network areas on an exclusive basis. In this case study of light rail systems, a set of mutually exclusive network-based buffers was required. To create such buffers, the authors developed a hierarchical raster-based algorithm. It is hierarchical in the sense that the off-network distance between each cell and its nearest network segment is calculated separately from the on-network distance between each segment and its nearest node. This method allows for the creation of buffers bounded by distance or travel cost with true mutual exclusivity and realistic allocation of off-network areas